Assiokktob



E.- L. CLARK.

PYROMETER.

APPLICATION HLED' 1ULY 23, 19KB.

Patented Aug. 12, 1919.

MTIVESSES: I INI/IENTOR' .3. WW EMERSON LVCLARK A 110mm EMERSON L. CLARK, OF LAKEWOOD, OHIO,

Q E l.

ASSIGNOR, BY MESNE ASSIGNMENTS, TO

NATIONAL CARBON COMPANY, INC., A CORPORATION OF NEW YORK.

PYRQMETE'R.

Specification of Letters Patent.

Patented Aug. 12, 1919.

Original application filed December 19, 1912, Serial No. 737,640. Divided and this application filed July 23,

1913. Serial To all whom it may concern:

Be it known that I, EMERSON L. CLARK, a citizen of the United States, residing at Lakewood, in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Pyrometcrs, of which the following is a full, clear, and exact description.

My invention relates to pyrometer systems and provides means for correcting inaccuracies due to change in temperature of cold junctions in the thermopile, as also described in my application Serial No. 7 37,640, filed December 19th, 1912, of which this application is a division.

In thermopiles the cold junctions generate E. M. F.s, but in a direction opposed to the E. M. F. of the hot junction. The E. M. F. impressed on the galvanometer is therefore less than that of the hot junction. Consequently allowance must be made for the E. M. F. of the cold junctions in using the thermopile to determine temperatures. If the temperature of the cold junctions is maintained constant the correction would be a simple matter as the galvanometer would be calibrated for the drop in E. M. F. caused by the counter E. M. F. However, the temperature of the cold junctions cannot easily be maintained constant in practice. It is, therefore, necessary to, provide means to compensate for such change in the temperature.

The manner in which the compensation is accomplished will be apparent from the following description, 'reference being had to the drawings in which,

Figure l is a view of one form of compensating system.

Fig. 2 diagrammatically illustrates the circuits of the system shown in Fig. 1.

Referring to Fig. 1, the thermopile here illustrated has a hot junction 1 and cold junctions 2 and 3. The cold junction 3 is connected through a resistance 'r' to one terminal 4 of the galvanometer and the cold junction Q'is directly connected to the other terminal 5. A galvanometer circuit is diagrammatically represented by the resistance 7 connected to these two terminals. A resistance 7 having a high positive temperature coeflicient has one terminal connected to the cold junction 2 and the other to the, binding post 4. This resistance is Wound around, or otherwise arranged in closeto the diagran'imatic representation shown in Fig. 2. \Vith the cold junction 2 and 3 at a certain temperature, say 24 degrees centigrade, the galvanometer will be calibrated to indicate the true E. M. F. of the hot junction 1. The scale reading, of course, can be calibrated to read directly in degrees, inasmuch as the E. M. F. is proportional to the temperature of the hot junction. However, if the temperature of the hot junction is unchanged and the ten'iperatures of the cold junctions be increased the resultant E. M. F. impressed on the galvanometer would be less were it nottor the compensating coil 1' in shunt to it. Since this coil is subjected to a like increase of temperature its resistance is increased. The increase of resistance in coil 1 diminishes the current flowing in the main line resistance 1' and thus diminishes the drop therearound. The decrease in drop compensates for the" decrease of voltage in the thermocouple and the Voltage impressed on the galvanometer remains constant. The galvanometer reading Will therefore be unaffected by the increase 1n' the temperature of the cold junction.

The compensation obtained by this arrangement can be made substantially exact only when the temperature of the hot junctions is unchanged. If the resistances are arranged to exactly compensate when the hot junction temperature is, say 900 degrees C. there will be over-compensation when the hot junction is at a temperature of say 1200 degrees C. for a like variation in the cold junction temperature when the hot junction is at a lower temperature, say 600 degrees C.- However, this arrangement Without any additional modifications more correctly indicates the temperature of the hot junctions than if the thermocouple had been connected directly to the galvanomcter without any compensating arrangement.

The system can be made to compensate more accurately for various temperatures of the hot junction by altering the resistances 1' r and 0 at. certain points in the galvanometcr reading. The two resistances 1- and 1 should be adjusted in such a way that they will always maintain substantially the same ratio to each other. That is, the ratio should remain substantially constant as the resistances are adjusted, it the resistance '2" does not meanwhile change in temperature. This change in 7' due to temperature changes, of course, changes the ratio. Since the calibration of the galvanometer requires that the equivalent re sistance of the circuit be the same, the re sistance 9- also is varied at the same time. In this way the over-compensation and under-compensation may be as small as desired. For a certain rise in the indication of the galvanometer due to increase in temperature of the hot junction, the resistance r and may be increased and the resistance 1' decreased a predetermined amount. On a decrease in indication the reverse change may be made. A scale A may be made on the rheostat to show .where the pointer B must be moved to adjust for changes in the ten'iperature of the hot junction. The changes may be made as line as desired. The resistance 1' may be varied by varying the resistance r" in circuit with it.

The resistances 1* and r are merely for the purposes of adjustment, as will be obvious from the previous explanation. For a small temperature range of hot junction te1nperature, the galvauometer will indicate the temperatures substantially correctly without these two adjustable resistances. In the drawing the resistances r and 1* are shown adjustable so that they can be reduced to Zero or increased to any desired amount to make the system properly adjustable for all ranges of hot junction temperature.

In Fig. 2 the resistance r is not shown as a separate resistance. This figure is a diagrammatic representation and the resistance 1' is shown adjustable itself. It will be obvious that adjusting the resistance r produces the same result as adjusting the re sistance r. In practice, however, it is much more preferable to have the separate resistance 1 to adjust the compensating coil circuit, as it is much easier to manipulate, and furthermore the active turns on the comiensating coil are then the same for all adustments.

Having described my lnvention, what I claim is:

1. In a pyrometer system, a galvanometer, a thermocouple, a resistance connected between the thcrmocouple, and galvanometer and a second resistance with a positive temperature cocilicient connected in shunt to the galvanomctcr, said resistances being pro-portioned to approximately compensate for temperature variations in the cold junction of said thermocouple for a predetermined temperature at the hot junction.

'2. In a pyrometer system, a. galvanometer, a thermocouple connected thereto by two leads, an adjustable resistance in one of said leads, and a resistance connected in shunt to the galvanometer responsive to temperature changes of the cold junctions of the thermocouple.

3. In a pyrometer system, a galvanometer, a thermocouple connected thereto by two leads, an adjustable resistance in one of said leads, a resistance having a positive temperature coetlicient of resistance connected in shunt to the galvanometer, said second resistance being located in close proximity to the cold junction of the thermocouple.

4.. In a pyrometer system, a galvanometer, a thermocouple, a resistance connected between the thermocouple and galvanometer, a second resistance with a positive temperature coefficient connected in shunt to the galvanometer, and means for varying the resistance of the circuit containing said second mentioned resistance.

5. In a pyrometer system, a galvanometer, a thermocouple, a resistance connected between the thermocouple and the galvanometer, :1, second resistance with a positive temperature coefficient connected in shunt to the galvanometer, and means for varying both of said resistances.

6. In a pyrometer system, a galvanometer having, a resistance, a thermocouple, a second resistance connected between the thermocouple and the galvanometer, a third resistance with a positive ten'iperature coetli-' cient located adjacent the cold junctions of said thcr1m couple and connected in shunt to the galvanometer, and means for simultaneously varying; all of said resistances.

7. In a pyrometer system, a galvanometer having a resistance, a thermocouple, a second resistance connected between the thermocouple and the galvanomcter, a third resistance with a positive temperature coefficient located adjacent the cold junctions of said thermocouple and connected in shunt to the galvanometer, and means for simultaneously increasing the galvanometer resistance while decreasing the second and third resistances.

8. In a pyrometer system, a galvanomet-er, a thermocouple, a resistance connected between the galvanoineter and one cold junction of the thermocouple, a compensating resistance located adjacent the cold junc tions of said thermocouple and connected 1n shunt to the galvanometer, means for ad justing said resistances, and a device 006p erating with said means to indicate the prcpcrtioned to correct individual characl0 teristics of the couple.

In testimony whereof, I hereunto aflii: my signature.

EMERSON L. CLARK. I

Witnesses H. G. GROVER, IRA J. ADAMS. 

